The decile system ranks schools by the socio-economic status of the areas where their families live.
Deciles are based on household incomes, occupations, educational qualifications, overcrowding and the proportion of people on benefits in a defined area where pupils live.
Each school provides a list of student addresses which is used to determine which areas each school is drawing its students from. Schools are ranked accordingly to five indicators of socio-economic status of communities the school's students live in.
Each school receives a score for each indicator and the 5 scores are added together. This total gives the school's standing in relation to all other schools. This then enables the Ministry of Education to place schools into 10 groups called 'Deciles'. These are ranked from highest to lowest, with approximately 10% of schools in each decile.